System for monitoring sensor outputs of a gas turbine engine

ABSTRACT

In a system for monitoring an output of a sensor for detecting an operating state of a gas turbine engine by comparing a value of an output of the sensor with a prescribed reference value, a calibration map for converting the output of the sensor into a variable that is normally used for controlling the engine is used for defining the reference value for determining the state of the sensor. Thereby, a fault of a sensor can be detected both accurately and promptly by using the existing resource without unduly complicating the control program. It is particularly desirable to monitor the output of the sensor by taking into account the current operating condition of the engine to improve the reliability in detecting a fault in the sensor.

TECHNICAL FIELD

The present invention relates to a system for monitoring the outputs ofsensors that detect various state variables of a gas turbine engine forthe purpose of detecting any abnormal condition in any one of thesensors.

BACKGROUND OF THE INVENTION

In an aircraft gas turbine engine, a large number of sensors areprovided in various parts thereof and the output values of these sensorsare used for optimally controlling the operation of the engine. A faultin any one of such sensors may cause abnormal values in the controlparameters, and prevents satisfactory operation of the engine.Therefore, it is highly important to take appropriate measures in caseof a sensor failure.

A fault of a sensor can be detected in come cases by comparing theoutput value of the sensor with a certain limit value or the change rateof the output value of the sensor with a prescribed threshold value. SeeJapanese patent laid-open publication No. 6-264767, for instance.

However, this known technology is only suitable for detecting misfirewhen starting the engine, and is not suitable for promptly detecting afault in a sensor during the normal steady-state and transient operationof the engine. Also, to permit detection of an abnormal output of eachone of a large number of sensors, a same number of reference maps as thenumber of the sensors are required for evaluating every one of thesensors. This undesirably increases the complexity of the controlprogram.

In the case of a gas turbine engine including a high pressure shaft anda low pressure shaft that are disposed in a coaxial relationship, it isalso known to define a prescribed relationship between the rotationalspeeds of the high pressure shaft and low pressure shaft, and judge thatat least one of the sensors is faulty when the output values of therotational speed sensors for the high pressure shaft and low pressureshaft deviate from the prescribed relationship beyond a certainthreshold. See Japanese patent laid open publication No. 2000-249629.

Again, this known technology is capable of achieving any reliabilityonly in a limited operating range, and is unable to detect a fault inthe sensors in the high speed and/or transient operating mode of theengine.

BRIEF SUMMARY OF THE INVENTION

In view of such problems of the prior art, a primary object of thepresent invention is to provide a system for monitoring the outputs ofsensors that detect various state variables of a gas turbine enginewhich allows a fault of the sensors to be detected both accurately andpromptly by taking into account the current operating condition of theengine.

A second object of the present invention is to provide a system formonitoring the outputs of sensors for detecting various state variablesof a gas turbine engine which allows a fault of the sensors to bedetected both accurately and promptly without unduly complicating thecontrol program.

A third object of the present invention is to provide a system formonitoring the outputs of sensors for detecting various state variablesof a gas turbine engine including a high pressure shaft and a lowpressure shaft that are disposed in a coaxial relationship which allowsa fault in one of the high pressure shaft rotational speed sensor andthe low pressure shaft rotational speed sensor to be detected bycomparing the reading of one of the sensors with a value that isestimated from the reading of the other in a reliable manner.

According to the present invention, at least part of the aforementionedobjects can be accomplished by providing a system for monitoring anoutput of a sensor for detecting an operating state of a gas turbineengine by comparing a value of an output of the sensor with a prescribedreference value, comprising: a calibration map for converting the outputof the sensor into a variable that can be used for controlling theengine, the prescribed reference value being defined in the calibrationmap.

Because the reference values are defined in association with thecalibration map which is used for the control of the engine, thecomplexity of the system can be minimized through the use of theexisting resource. In particular, if the system further comprises meansfor detecting a current operating mode of the engine, and the prescribedreference value is varied depending on the current operating mode, themonitoring of the sensor can be executed in a highly precise andefficient manner so that an unexpected behavior of the engine can beensured and the reliability of the engine can be enhanced. According toa preferred embodiment of the present invention, the current operatingmode of the engine may be detected by comparing the output value of thesensor with an operating mode detecting value defined on the calibrationmap.

According to another aspect of the present invention, there is provideda system for monitoring an output of a sensor for detecting an operatingstate of a gas turbine engine including a high pressure shaft and a lowpressure shaft disposed in a coaxial relationship by comparing a valueof the output of the sensor with a prescribed reference value,comprising: a low pressure shaft rotational speed sensor for detecting arotational speed of the low pressure shaft; a high pressure shaftrotational speed sensor for detecting a rotational speed of the highpressure shaft; an inlet air temperature sensor for detecting atemperature of air at an inlet end of the engine; estimating means forestimating a rotational speed of the low pressure shaft according to anoutput of the high pressure shaft rotational sensor and an output of theinlet air temperature sensor; comparing means for comparing an estimatedvalue of the rotational speed of the low pressure shaft estimated by theestimating means and an output of the low pressure shaft rotationalspeed sensor; and determining means for detecting a fault in the lowpressure shaft rotational speed sensor according to a result ofcomparison by the comparing means.

Thereby, should the low pressure shaft rotational speed sensor fail, itwould be possible to detect it promptly by comparing the output of thelow pressure shaft rotational speed sensor with an estimated value ofthe low pressure shaft rotational speed based on the output of the highpressure shaft rotational speed sensor and output of the inlet airtemperature sensor so that the reliability of the engine control can beenhanced. In particular, if the comparing means compares the estimatedvalue of the rotational speed of the low pressure shaft estimated by theestimating means and the output of the low pressure shaft rotationalspeed sensor only when the estimated value is greater than a prescribedvalue, it becomes possible to simplify the sensor fault detectingprocess, and this is particularly beneficial where there are two or morelow pressure shaft rotational speed sensors.

The foregoing feature can also be implemented by exchanging the lowpressure shaft rotational speed sensor and high pressure shaftrotational speed sensor with each other, and using an appropriate mapfor estimating the output of the low pressure shaft rotational speedsensor or the high pressure shaft rotational speed sensor as the casemay be.

BRIEF DESCRIPTION OF THE DRAWINGS

Now the present invention is described in the following with referenceto the appended drawings, in which:

FIG. 1 is a diagram of a gas turbine engine including a system embodyingthe present invention;

FIG. 2 is a graph showing the mode determination values on a calibrationmap for the output of a throttle lever angle sensor;

FIG. 3 is a graph showing the mode determination values on a calibrationmap for the output of a high pressure shaft rotational speed sensor;

FIG. 4 is a flowchart of the process of monitoring sensor outputsaccording to the present invention;

FIG. 5 is a graph showing the tolerable range of the calibrated value ona calibration map for the output of a certain sensor;

FIG. 6 is a graph showing the tolerable range of the calibrated value ona calibration map for the output of another sensor;

FIG. 7 is a diagram of a gas turbine engine incorporated with a secondembodiment of the present invention; and

FIG. 8 is a flowchart of the control process of the second embodiment ofthe present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 schematically illustrates a gas turbine engine to which thepresent invention is applied. This gas turbine engine 1 comprises a highpressure shaft 4 carrying a compressor rotor 2 and a high pressureturbine wheel 3, and a low pressure shaft 7 carrying a low pressureturbine wheel 5 and a fan 6. A combustion unit 17 is providedimmediately upstream of the high pressure turbine. The instrumentationof this engine comprises a high pressure sensor 8 for measuring theoutlet pressure P3 of the compressor, a low pressure sensor 9 formeasuring the inlet pressure of the fan 6, a high pressure shaftrotational speed sensor 10 for measuring the rotational speed N2 of thehigh pressure shaft 4, a low pressure shaft rotational speed sensor 11for measuring the rotational speed N1 of the low pressure shaft 7, ahigh temperature sensor 12 for measuring the inlet temperature of thehigh pressure turbine, an inlet air temperature sensor 13 for measuringthe temperature of air at the inlet end of the engine and a throttlelever angle sensor 14 for detecting the angular position of a throttlelever. A fuel supply control unit 15 controls a fuel metering valve 16that supplies fuel to the combustion unit 17 according to the outputsfrom these sensors so that the engine may operate under an optimumcondition at all times.

These sensors 8 to 14 are monitored by a sensor monitoring system so asto detect an abnormal output from any one of the sensors and takeappropriate measures if such an abnormal output is detected. In theillustrated embodiment, the monitoring of the sensors takes into accountthe current operating mode of the engine. For this purpose, the sensormonitoring system comprises an operating mode determining unit 21, areference value determining unit 22 and a sensor abnormal conditiondetermining unit 23. The sensor monitoring system also makes use ofcalibration maps 24 that are provided for the purpose of converting theoutputs of various sensors into calibrated values suitable for use asinputs for controlling the engine.

The operating mode determining unit 21 is adapted to identify thecurrent operating mode of the engine by comparing the outputs of thesensors such as the throttle lever angle sensor 14 and high pressureshaft rotational speed sensor 10 with the corresponding modedetermination values that are defined on the corresponding calibrationmaps 24 (FIGS. 2 and 3).

The operating modes of the engine include start ST, low loadsteady-state LR, acceleration AC, high load steady-state HR,deceleration DC and emergency fuel cut CO modes. Only the maps for theoutput values of the throttle lever angle sensor 14 and the highpressure shaft rotational speed sensor 10 are mentioned in theillustrated embodiment in connection with the determination of thecurrent operating mode, but the accuracy of mode determination can beimproved by alternatively and/or additionally taking into account theoutput values of a speed meter and an altitude meter and a predeterminedflight schedule as well as the outputs of the other sensors.

The control flow of the process for determining an abnormal condition ofthe sensor outputs is now described in the following with reference toFIG. 4.

First of all, the operating mode determining unit 21 determines thecurrent operating mode from the start ST, low load steady-state LR,acceleration AC, high load steady-state DC, deceleration DC andemergency fuel cut CO modes (step 1). Because the operating mode isnecessarily the start mode at the beginning of the control flow, thereference values corresponding to the start mode are read out at thebeginning of the control flow (step 2). The output values of the varioussensors are read when the start switch is pressed (step 3), and arecompared with the corresponding reference values to determine if theyfall within prescribed tolerable ranges.

If the output values of the sensors are determined to be all within theprescribed tolerable ranges in step 4, as it means that the sensors areall in proper order, the normal start control is continued according tothe outputs of the sensors (step 5). If any one of the output values isdetermined to be outside the corresponding prescribed tolerable range,an alarm is issued to indicate a fault in the sensor, and acountermeasure control mode corresponding to the failure of the sensoris selected for the operation of the engine (step 6). Suchcountermeasure control modes include (1) the use of a secondary sensoror a secondary CPU, (2) the use of an estimated value based on theoutputs from other sensors instead of the output value of the faultysensor, and (3) the use of a prescribed fixed value instead of theoutput value of the faulty sensor.

Once the engine has started, the operating mode of the engine changesfrom one mode to another as the time progresses. The operating modedetermining unit 21 takes into account the output values of the throttlelever angle sensor 14 and the high pressure shaft rotational speedsensor 10 when determining the current operating mode of the engine.More specifically, the operating mode determining unit 21 marks thecorresponding reference values on the calibrated values of thecalibration maps (FIGS. 2 and 3) for these sensors 10 and 14, and looksup these maps to determine the current mode by comparing the calibratedvalues with the reference values. The operating mode determining unit 21additionally takes into account the output values of a speed meter andan altitude meter and a predetermined flight schedule among othervariables to exactly determine the current operating mode.

Once the operating mode is determined, the reference value determiningunit 22 marks the corresponding tolerable range of each sensor on thecorresponding calibration map, and determines if the output of eachparticular sensor is within the prescribed tolerable range.

In the case of the inlet pressure P1 of the fan, outlet pressure P3 ofthe compressor 2 and inlet temperature T3 of the turbine, thecalibration map for applying the reference values is given asrepresented in FIG. 5. In other words, in these cases, the calibrationcurve includes a central linear region having a certain inclination andregions of a greater inclination that are connected to either end thecentral region. The regions of the greater inclination allow detectionof abnormal output values of the corresponding sensor at a highersensitivity because the calibration value changes more rapidly or morepronouncedly than the output value of the sensor. The calibration curveincludes a saturated region in the upper (larger) end of the curve toprevent an output value of an excessive level from being transmittedfrom the sensor to the control system.

In the case of the rotational speed N1 of the low pressure shaft 7 androtational speed N2 of the high pressure shaft 4, the calibration mapfor applying the reference values is given as represented in FIG. 6. Inother words, in these cases, the calibration curve includes a mainlinear region having a certain inclination extending from a low valueregion and a region of a greater inclination that is connected to thehigh value end the main region. The region of the greater inclinationallows detection of abnormal output values of the corresponding sensorsbecause the calibration value changes more rapidly and more pronouncedlythan the output value of the sensor. The saturation region connected tothe high value end of the region of the greater inclination similarlyprevents an output value of an excessive level from being transmittedfrom the sensor to the control system.

These calibration maps convert the output value of each sensor(abscissa) to a corresponding calibrated value (ordinate), and are usedfor converting the output values of the various sensors to values thatare suitable for use as control parameters of the engine. In theillustrated embodiment, the reference values and prescribed toleranceregions are defined on the ordinate of each calibration map.

Because the output of each sensor may contain noises, a single samplingof an output value may not represent the output value. It is thereforepreferable to compare two or more sample values and evaluate thefluctuations in the sampled value. The magnitude of the fluctuations maybe taken into account so that the evaluation of the status of eachsensor may be performed in an optimum fashion.

FIG. 7 shows a gas turbine engine that is incorporated with a secondembodiment of the present invention. The parts corresponding to those ofthe previous embodiment are denoted with like numerals without repeatingthe description of such parts.

This embodiment further comprises an estimating unit 31 for estimatingthe rotational speed of the low pressure shaft 7 from the outputs of thehigh pressure shaft rotational speed sensor 10 and inlet air temperaturesensor 13, a determining unit 32 for determining if the low pressureshaft rotational speed sensor 11 is operating properly and a selectorunit 33 for selecting between the output from the low pressure shaftrotational speed sensor 11 and the output from the estimating unit 31.

More specifically, the estimating unit 31 generates a reference valueN1S which is to be compared with the output N1 from the low pressureshaft rotational speed sensor 11 to determine if there is any fault inthe low pressure shaft rotational speed sensor 11. This reference valueN1S is obtained by modifying the rotational speed N2 of the highpressure shaft 4 detected by the high pressure shaft rotational speedsensor 10 with the inlet air temperature T1 at the inlet of the engine,or more specifically at the inlet of the fan 6 measured by the inlet airtemperature sensor 13, and feeding this modified rotational speed N2C ofthe high pressure shaft 4 to a calibration map incorporated in theestimating unit 31. The calibration map may consist of one provided forthe purpose of converting the output of a sensor into a calibratedvalues suitable for use as an input for controlling the engine.

Preferably, the estimating unit 31 may be incorporated with a pluralityof such maps for different operating modes such as stead-state,accelerating and decelerating modes so that one of such maps may beselected for use depending on the current operating mode of the engine.In the illustrated embodiment, the modified rotational speed N2C of thehigh pressure shaft is given by the following formula:N2C(N2, T1)=N2/{(T1+273.15)/288.15}^(1/2)  (1)

FIG. 8 shows the control process for detecting a fault in the lowpressure shaft rotational speed sensor 11.

First of all, the output value N2 of the high pressure shaft rotationalsensor 10 is forwarded to a fault detecting unit 34 for the highpressure shaft rotational speed sensor 10 (step 21) and is determined ifit is normal or not (step 22). This can be effected by sampling theoutput value of the high pressure shaft rotational sensor 10 at every 10msec and comparing each sampled value with a prescribed threshold value.If any of the sampled value exceeds this threshold value, it isdetermined that the high pressure shaft rotational sensor 10 is faulty.

If no fault is found with the high pressure shaft rotational sensor 10,the output value N2 of the high pressure shaft rotational sensor 10 isforwarded to the estimating unit 31, and is used for looking up thereference value N1S from the map (step 23). If the high pressure shaftrotational sensor 10 was found to be faulty in step 22, an alarm isissued to indicate this and the control action is terminated in step 24.

Following step 23, it is determined if the reference value N1S iscompared with a certain prescribed threshold value Nth (the idlingrotational speed of 3,000 rpm, for instance) in step 25. If thereference value N1S is less than the prescribed threshold value Nth, theprogram flow returns to step 21. If the reference value N1S is greaterthan the prescribed threshold value Nth, the output N1 of the lowpressure shaft rotational sensor 11 is compared with reference value N1Sin step 26. The difference between the output N1 of the low pressureshaft rotational sensor 11 and reference value N1S is compared with aprescribed tolerance value in step 27. If this difference is within theprescribed tolerance value, the low pressure shaft rotational sensor 11is determined as being normal, and the selection unit 33 selects theoutput of the low pressure shaft rotational sensor 11 for use in thecontrol of the engine (step 28). Conversely, it this difference isbeyond the prescribed tolerance value, the selection unit 33 selects theoutput N1S of the estimating unit 31 for use in the control of theengine (step 29).

Thus, according to the present invention, even when there is a fault inthe low pressure shaft rotational speed sensor 11 for detecting therotational speed of the low pressure shaft 7, by generating a substituteoutput N1S for the sensor which allows the engine to be operated in astable manner and in a manner that suits the current operating mode, anysudden change in the behavior of the engine can be avoided.

In particular, if the comparing means compares the estimated value N1Sof the rotational speed of the low pressure shaft estimated by theestimating means with the output N1 of the low pressure shaft rotationalspeed sensor 11 only when the estimated value N1S is greater than aprescribed value Nth as given in steps 25 and 26, it is possible todetect a fault even when both the sensors have become faulty without anydifficulty even in a low speed range.

The foregoing embodiment used only one low pressure shaft rotationalspeed sensor 11, but it is also possible to use two low pressure shaftrotational speed sensors 11 and compare the output values of the twosensors for the purpose of improving the reliability. In a low speedrange, because the absolute values of the two low pressure shaftrotational speed sensors are small, the difference between them in caseof a failure in one of the sensors will be correspondingly small, and itis therefore relatively difficult to detect a fault in a low speedrange. However, when the foregoing embodiment is applied to a case wheretwo ore more low pressure shaft rotational speed sensors 11 are used, itis possible to detect a fault in one of the sensors both accurately andpromptly without unduly complication the arrangement even in a low speedrange.

Although the present invention has been described in terms of preferredembodiments thereof, it is obvious to a person skilled in the art thatvarious alterations and modifications are possible without departingfrom the scope of the present invention which is set forth in theappended claims. For instance, the low pressure shaft rotational speedsensor and high pressure shaft rotational speed sensor may beinterchanged with each other in the foregoing embodiment. In such acase, an appropriate map for estimating the output of the high pressureshaft rotational speed sensor will be used.

The contents of the original Japanese patent applications on which theParis Convention priority claim is made for the present application areincorporated in this application by reference.

1. A system for monitoring an output of a sensor for detecting anoperating state of a gas turbine engine by comparing a value of anoutput of the sensor with a prescribed reference value, comprising: acalibration map for converting the output of the sensor into a variablethat can be used for controlling the engine, the prescribed referencevalue being defined in the calibration map.
 2. The system for monitoringan output of a sensor according to claim 1, wherein the system furthercomprises means for detecting a current operating mode of the engine,and the prescribed reference value is varied depending on the currentoperating mode.
 3. The system for monitoring an output of a sensoraccording to claim 2, wherein the system is adapted to detect thecurrent operating mode of the engine by comparing the output value ofthe sensor with an operating mode detecting value defined on thecalibration map.
 4. A system for monitoring an output of a sensoraccording to claim 1, wherein the gas turbine engine includes a firstshaft and a second shaft disposed in a coaxial relationship; the systemfurther comprising: a first shaft rotational speed sensor for detectinga rotational speed of the first shaft; a second shaft rotational speedsensor for detecting a rotational speed of the second shaft; an inletair temperature sensor for detecting a temperature of air at an inletend of the engine; estimating means for estimating a rotational speed ofthe first shaft according to an output of the second shaft rotationalspeed sensor and an output of the inlet air temperature sensor;comparing means for comparing an estimated value of the rotational speedof the first shaft estimated by the estimating means and an output ofthe first shaft rotational speed sensor; and determining means fordetecting a fault in the first shaft rotational speed sensor accordingto a result of comparison by the comparing means.
 5. A system formonitoring an output of a sensor according to claim 4, wherein the firstshaft consists of a low pressure shaft and the second shaft consists ofa high pressure shaft.
 6. The system for monitoring an output of asensor according to claim 5, wherein the comparing means compares theestimated value of the rotational speed of the low pressure shaftestimated by the estimating means and the output of the low pressureshaft rotational speed sensor only when the estimated value is greaterthan a prescribed value.